Subnet Mask

Our admin and curriculum servers share the same network and the subnet mask was 255.255.255.0. When we had county broadband installed they didn't mention changing this but the LEA support team recommended changing the admin subnet to 255.255.252.0. I need more curriculum IP addresses so I asked the County Broadband team about changing the curriculum subnet and they said it should be 255.255.252.0 However, I'm considering changing it to 253.0 which will give me more than enough IP addresses and will help segregate the admin and curriculum systems. Does this make sense or am I barking?

253.0 is verboten! you can do 252.0 or 254.0, but not 253, because of the way the bits fall. A quick cuttypasty from a recent thread:

Quote:

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... That is, you can have a subnet mask of (say) 255.255.252.0 which will give you approx 4 times your current address space:

11111111.11111111.11111111.00000000 = 255.255.255.0 - current setting
11111111.11111111.11111110.00000000 = 255.255.254.0 - ~2x as many hosts
11111111.11111111.11111100.00000000 = 255.255.252.0 - ~4x as many hosts
11111111.11111111.11111000.00000000 = 255.255.248.0 - ~8x as many hosts

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The possible problems are that the larger ip address range you want might overlap with another school and therefore you can't have it.

They might be willing to give you a completely different range to work with - liaise with them but be assertive about your ip range needs and see what they offer you.

regards

Simon

For the sake of your sanity I cannot stress enough that you get them to confirm the range they give you is NOT in use by another school.

In the summer I requested an entirely new larger range. So I ring the LEA IT boys up "of course sir, here's your new IP range. Let me just check our Excel 97 spreadsheet to make sure it's not allocated to another school. Ah, it isn't. enjoy". 2 weeks later at the start of term,our printers are spewing out crap from other schools. Turns out they hadn't updated their little spreadsheet for a while and had given us someone elses range!!

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Originally Posted by TeddyKGB

For the sake of your sanity I cannot stress enough that you get them to confirm the range they give you is NOT in use by another school.

In the summer I requested an entirely new larger range. So I ring the LEA IT boys up "of course sir, here's your new IP range. Let me just check our Excel 97 spreadsheet to make sure it's not allocated to another school. Ah, it isn't. enjoy". 2 weeks later at the start of term,our printers are spewing out crap from other schools. Turns out they hadn't updated their little spreadsheet for a while and had given us someone elses range!!

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LOL - oh thats a classic.... :D:D
Nothing like a 'change management process' is there ?

You should be using non routable IP addresses
that way the school down the road could be using exactly
the same addresses and it wouldn't matter. Your LEA/Council
would then map your internal default gateway to external ones
via their firewall ( the same way your broadband works at home but
just on a bigger scale )

see

http://mtmnet.com/PDF_FILES/NonRoutableIPaddresses.PDF

no way in the world should someone be able to print to your printers
of even ping an address on your network. If you use one of these
reserved addresses you can have a subnet mask of something
like 255.255.0.0 and have loads of addresses

If you are using real (as in routable) ip addresses then you'd better know
exactly what you are doing. If your LEA/Council are telling you to use
routable ip addresses and giving out overlapping or already used ip
addresses then they need to be taken out into the playgound and beaten up

M

It makes perfect sense bar the 3, if the admin machines are already using this subnet mask then the stations will have spread out into this new address space already and should have thrown some errors by now.

- Using information from your previous post -
Your address space with a subnet mask of 255.255.252.0 is between 10.91.4.1 and 10.91.7.254 this gives you 1022 avalible addresses all in the same subnet. The ip broadcast address is 10.91.7.255 and the network address is 10.91.4.0 .

What i find really difficult is that the LEA or service provider goes all the way to the wqorkstation ip address level where they should just terminate the connection at the permiter of the school's network. This way the school can design and use thier own IP addressing scheme without any effect on other schools etc. There is absolutely no need for RBCs or LA to go down to the workstation level on the school's PCs. I understand from filtering control but still think they should just leave it at the permiter and allow schools to NAT their connections.

I've seen so many implementation where the overlap in IP addresses has caused so much confusion and ongoing troubleshooting.

Ash.

Quote:

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Originally Posted by SYNACK

It makes perfect sense bar the 3, if the admin machines are already using this subnet mask then the stations will have spread out into this new address space already and should have thrown some errors by now.

- Using information from your previous post -
Your address space with a subnet mask of 255.255.252.0 is between 10.91.4.1 and 10.91.7.254 this gives you 1022 avalible addresses all in the same subnet. The ip broadcast address is 10.91.7.255 and the network address is 10.91.4.0 .

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The above IP range uses CIDR method (classless).

Ash.

We're currently on a subent of 10.4.28.xxx /23 giving us 510 pssoble hosts....

but we're running out - what iwth PCs, servers, and various other IP devices (printers, cameras, etc..) so in process of moving to a new range of 192.168.1.1 to 192.168.9.254

With servers, printers, etc on the 192.168.0.xx range..

Just need to get Smoothwall to allow computers through on that range - if i can get the internal alias properly configured..

Quote:

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Originally Posted by ashok

What i find really difficult is that the LEA or service provider goes all the way to the wqorkstation ip address level where they should just terminate the connection at the permiter of the school's network. This way the school can design and use thier own IP addressing scheme without any effect on other schools etc. There is absolutely no need for RBCs or LA to go down to the workstation level on the school's PCs. I understand from filtering control but still think they should just leave it at the permiter and allow schools to NAT their connections.

I've seen so many implementation where the overlap in IP addresses has caused so much confusion and ongoing troubleshooting.

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This is true, and I agree. But I also agree with and accept that the LEA distributes address ranges. NAT'ing isn't possible here due to various technical and political reasons and I'm guessing other establishments have the same problem. I do recall in the BECTA technical specs that the LEA or RBC should be responsible for address ranges.

Problems only ocurr such as in my case they hadn't been keeping their documentation up to date.

Quote:

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Originally Posted by ashok

What i find really difficult is that the LEA or service provider goes all the way to the wqorkstation ip address level where they should just terminate the connection at the permiter of the school's network. This way the school can design and use thier own IP addressing scheme without any effect on other schools etc. There is absolutely no need for RBCs or LA to go down to the workstation level on the school's PCs. I understand from filtering control but still think they should just leave it at the permiter and allow schools to NAT their connections.

I've seen so many implementation where the overlap in IP addresses has caused so much confusion and ongoing troubleshooting.

Ash.

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Ofcourse overlapping ip address space isn't an issue when MPLS VPN's and VRF tables are deployed in the WAN. Although i'd imagine you can count on the digits on one hand the number of authorities who've transitioned to MPLS VPN's - most are probably still stuck on the p2mp hub and spoke model and eigrp routing.

Quote:

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Originally Posted by SYNACK

It makes perfect sense bar the 3, if the admin machines are already using this subnet mask then the stations will have spread out into this new address space already and should have thrown some errors by now.

- Using information from your previous post -
Your address space with a subnet mask of 255.255.252.0 is between 10.91.4.1 and 10.91.7.254 this gives you 1022 avalible addresses all in the same subnet. The ip broadcast address is 10.91.7.255 and the network address is 10.91.4.0 .

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We have static addressing throughout at present, hence my reason for wanting more addresses. So everything will still be within the range 10.91.4.1 - 255. If you read my previous post, I never managed to get DHCP to run on the curriculum server and ran out of time so I just stuck with static addresses. That has become more of a bind as the network has grown, so I plan to spend the holidays sorting out DHCP. What I then want to do is create a DHCP range big enough to take all of the curriculum computers (150 will do) and then I can just go round and reset the computers to DHCP at my leisure. So if I read this right, 255.255.254.0 will give me 10.91.5.1-255 to play with?

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Originally Posted by laserblazer

So if I read this right, 255.255.254.0 will give me 10.91.5.1-255 to play with?

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A 255.255.254.0 mask will give you 510 addresses in the address space. the starting ip depends on what you get allocated.

.255.0 = 254 hosts
.255.128 = 126 hosts

As sahmeepee said its all about the binary

Didn't remember that you had said that you went static, just recalled that I had given an answer to a similar question http://www.edugeek.net/forums/showth...t=14946&page=2

Sorry, I should have said extra IP addresses.